1. Field of the Invention
The present invention relates to a sensor arrangement for detecting moisture and/or [water] drops on a window, in particular a windshield of a motor vehicle, according to the preamble of claim 1.
2. Description of the Background Art
Sensor arrangements are used in automobiles, for example, in order to control automatic windshield wipers and/or fans.
DE 196 02 345 A1 discloses a sensor for detecting the moisture on a window of a motor vehicle in which at least one electrically conductive layer is arranged in a certain pattern on an exterior surface of the window. The sensor evaluates the electrical resistance which is present between two layers with different electrical potentials and which changes as the quantity of water on the window changes.
DE 101 52 998 C2 describes a sensor unit for detecting wetting of a window having two sensors that operate on the capacitive principle. One of the sensors is for detecting condensation on the inside of the window, and the other is for sensing condensation on the outside. The sensors are connected to an analysis unit that is integrated in the sensor unit.
DE 197 23 858 A1 describes a device for heating a window in which a window heater is controlled as a function of wetting of the window. This wetting is detected by a moisture sensor, which takes the form of a capacitive sensor, for example.
From EP 710 593 A1 is known a sensor for capacitive measurement of the density of moisture on a window. Arranged on a side of the window facing away from the liquid, or inside the window, are conductive traces that form a capacitor and have a comb-like or finger-like structure. The conductive traces are connected to a measurement device for determining the capacitance.
In none of the known sensors from the prior art cited above is temperature compensation mentioned.
The applicant is aware of temperature compensation for a capacitive rain sensor in which a temperature of the window is measured by means of a separate temperature sensor—for example a resistance thermometer—and is added as a correction value to the capacitance present at the rain sensor. This temperature compensation requires a separate sensor and a relatively great computational effort.